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Full text of "The Cambridge Natural History"

ing therefore a less .specialised condition of the limbs. It is
aix interesting fact that the aiujulation of the limbs is to some
extent obliterated iu very bulky crea turns, and almost, entirely
so in the elephants (see p. 217), which wcm to need strong and
straight pillars for the due support of their huge bodies.
The alertness and general intellectual superiority of mammals
to all animals lying below them in the series (with the exception,
of the birds, which are in their way almost on a level with the
Mammalia) are seen by their active, and eonthnious movements.
The lengthy periods of absolute motionlcHsneHM, KO familiar to
everybody in such a creature as the Crocodil**, art* unknown amooj^
the more typical Mammalia, excerpt indeed during slerp. This
mental condition is clearly shown by the proportionate develop-
ment of the external partn of all the organs of the, higher .sense**.
The Mammalia as a rule have well-developed, often extremely
large, flaps of skin surrounding the entrance to the orjjjuu of
hearing, often called " ears/* but better termed "pinnae," Thoae
are provided with special muHelen, anil can IKS often moved and
in many directions. The nose, i always^ or nearly always, very
conspicuous by its naked character; by the large, nut face, often
moist, which mirrounds tho noKtriln ; and again by the. niUHcl<',
which enable this tracts of the integument to 1m moved ut will.
The eyes, perhaps, are lesn marked in their priuioitiiuaxuut over the
eyes of lower Vertebrates than art* the earn and nom*;, but they
are provided as u rule with uppi^r and lower t>y*litls, a will UH
by a nictitating membrane a In lower Vertebrat;eH. Tim uppart^tit
predominance of the seufuu* of Hmeil itntl hiuiriit^ <>vor that of
siglit appears to be marked in this Mammalia* and may account
for their divernity of voice a well a of odour, iincl ft>r the
general sani6xi<30B of coloration which diHting-wislteH thin g;r*t!p
from, the brilliantly-coloured bird and reptiltw. Tim li**iitt, ttw
which bears these or^wis of special *m8t% is mon*. obviouHly
marked otifc from the neck and body than in th<s ease with the
duller creattires occupying the lower bruncluw of the Vertebrate
stem.
Th Hair.The Mammalia are absolutely ilistiiigtiwlwwl frtwn
all other Vertebrates (or, for the mutter of that, InverUibruiwH)
by the pOBSession of hair. To define a nmmYual as u Vortebrattt
with hair would be an entirely excluniva deftnition ; even in the
smooth Whales a few* huixw fc least are present^ which may l*e